1. Field of the Invention
The present invention relates to thermally responsive valve devices. More particularly, the present invention relates to thermally responsive valve devices having valve members actuated by a thermostat to control fluid communication between a pluralitv of ports.
2. Prior Art
Various thermally responsive valve devices have been proposed for controlling the flow of oil which is transmitted to an oil cooler for vehicle engines. In this way, the optimum temperature of the oil can be maintained and a high load on the oil cooler can be prevented. One type of thermally responsive valve device is illustrated in FIG. 4.
With reference to FIG. 4, a body 2 of the thermally responsive valve device 1 has an oil inlet port 3 and first and second outlet ports 4 and 5. The inlet port 3 is connected to an oil pump 8 while the first outlet port 4 is directly connected to a vehicle engine E and the second outlet port 5 is connected to an oil cooler C which is connected to the engine E. A spool valve 8 is slidably received within a bore 6 of the body 2 and is biased to the left (as seen in the FIG. 4) by a spring 7. The spool valve 8 is urged to the right (as seen in FIG. 4) by a temperature responsive device or thermostat 9 such as a thermally responsive wax type thermostat.
The spool valve 8 is normally maintained in the illustrated position in which the inlet port 3 is in fluid communication with the first outlet port 4. In response to an increase in temperature, the wax within the thermostat 9 expands to urge the spool valve 8 to move to the right (as seen in FIG. 4) against the biasing force of the spring 7 whereby the fluid communication between the ports 3 and 4 will be correspondingly reduced and the fluid communication between the inlet port 3 and the second outlet port 5 will be correspondingly increased. Thus, at least a portion of the oil is transmitted to the engine E through the cooler C.
In this type of thermally responsive valve device, the oil may leak from the inlet port 3 to the first outlet port 4 through the clearance between the inner surface of the bore 6 and a land portion of the spool valve 8 even when the spool valve 8 is moved completely to the right. The above-described leakage of the oil may increase when the viscosity of the oil is decreased due to high temperature conditions and may also increase when the flow resistance in the oil cooler C increases. Therefore, the desired flow of fluid (oil) through the cooler C may not be obtained.